Method and article for printing and engraving



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July 15, 1969 l J. E. SMITH 3,455,239

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July l5, 1969 J. E. SMITH 3,455,239

METHOD AND ARTICLE FOR PRINTING AND DNGRAVING Filed May 2, 1966 3Sheets-Sheet 3 llls 3,455,239 METHOD AND ARTICLE FOR PRINTING ANDENGRAVING James E. Smith, Avon, Conn., assignor to United AircraftCorporation, East Hartford, Conn., a corporation of Delaware Filed May2, 1966, Ser. No. 546,996 Int. Cl. B41n 1/00; G01d 15/10; G03f 7/00 U.S.Cl. 101-395 20 Claims ABSTRACT OF THE DISCLOSURE This invention relatesto a method of making printing plates, a blank printing plate employedin the method, and the product of the method. An electron beam is sweptacross the surface of the blank printing plate having a plurality ofuniformly shaped projections to selectively remove the projections andleave printing intelligence on the blank. The projections aresuficiently small and so densely packed that the projections can imparthigh resolution, half-tone characteristics to the blank. A printingplate made from the blank plate can print both text material andpictorial material in greytones. Widely separated, individualprojections may be preserved at otherwise void areas of the plates tosupport the printed page during the printing process.

This invention relates to a plate for printing and the method forproducing it. More specifically it relates to a plate for halftoneprinting with high quality resolution.

Most engraving or etching processes used today are aimed at producing astipple pattern of either minute projections or depressions on anengraving plate. The engraved patterns then consist of arrays of verysmall holes or projections which simulate the intelligence beingreproduce-d on the printing plate. The degree of fidelity which can beachieved and the faithfulness of the tone which can be accomplished inthe reproduction heavily depends upon the resolution in these arrays ofdots. For example, if large dots are used they must generally be fairlywidely spaced. The word dots is used here in a generic sense to indicateink carrying areas such as small depressions, cavities, projections,etc., irrespective of the shape of the dots which can, of course, beeither round, rectangular or any other convenient shape. The number oflarge surface area dots which can occupy a given area on the plate isquite limited, and a large dot array would appear to the eye as a verycoarse pattern. On the other hand, if the dots are small, more of themcan be packed into a given area and the dot array would then appear as afine pattern. In fact, if the dots are extremely small and denselypacked, the pattern would appear to the eye as one continuous tone inwhich the eye could no longer distinguish the individual dots. Obviouslythen, if one could carry the dot representtation to its extreme, forexample using millions of microscopic dots in a closely packed array,even very small ordinary text letters in addition to the customarypictorial material could be reproduced faithfully, clearly and with goodresolution.

The techniques available today to produce such closely packed arrays aregenerally slow, require meticulous care in their application, and theirresolution is limited to pictorial displays and large text letters, butcannot be used with very small text letters. Hence, today highresolution dot arrays have not been used to any extent wherein time oreconomics play a dominant role.

The high resolution capabilities of energized beams such as lasers andincluding charged particle beams such as electron or ion beams can be assmall as one micron or less and have demonstrated their utility invarious l United States Patent elds such as microscopy, microchemistry,and precision cutting or welding of a variety of materials. Thedemonstrated capabilities of the energized beam in achieving extremelyhigh lpower densities would ordinarily lead one to assume that vit canbe used with convenience in a high speed engraving system which couldproduce a printing plate having a closely packed dot array by utilizingthe beam as a cutter or evaporator. However, there are a number ofproblems associated with using an energized beam for these purposeswhich to date have inhibited the application thereof to themanufacturing of printing plates.

The use of an electron beam for cutting various materials by evaporationmethods, is well known as for instance described in the patent toSteigerwald, No. 2,793,281. The method of reproducing an image with anelectron beam by melting is described in the patent to Groak, No.2,630,484. The production of a printing plate with a laser beam isdescribed in an article by William T. Reid entitled Laser-EtchingPrinting Plates May Soon Be a Reality, Inland Printer/AmericanLithographer, December, 1964, pages 57 and 113. The patent to Griswold,No. 2,107,294, discloses any intaglio printing plate having cells withnarrow walls and wherein the material in the cells responds chemicallydifferently to an etch bath compared to the Walls which aresubstantially impervious to the bath. The use of an energized beam tocut printing plates and write thereon as disclosed in the prior art isgenerally slow in comparison with chemical methods of producing aprinting plate. This is due to the fact that a large amount of materialmust be removed within a very short time by the energized beam.

The chemical etching art, which is a large-area material removal processas in contrast with the energized beam point-by-point removal process,has been applied in the production of printing plates for many years.Despite the fact that extremely high power densities, for instance 109watts per square inch can be achieved with energized beams, thepoint-to-point approach of the energized beam cutting methods poses somereal and practical problems when one tries to achieve high plate makingspeeds comparable with the chemical etching art.

Some insight can be obtained to this problem by reviewing the phenomenaactually involved. For instance, when an energized beam strikes theworkpiece as in FIGURE 13, the thermal energy transferred to theworkpiece is free to spread outward and downward from the point ofimpingement due to the thermal conductivity of the material constitutingthe workpiece. Thermal conduction continues as long as the thermalgradients persist and there is a path for the heat to flow away from thepoint of impingement. As the material in the impingement larea becomesvaporized, which occurs rather rapidly due to the high power density ofthe beam, the thermal conductive path from the center of the beamimpingement area to the periphery of the hole is broken. This doe-s notmean necessarily that the thermal energy transferred to the holeperiphery or the surrounding material has ceased. In fact, thermaldiffusion through the vapor created as Well as the radiant heat transferpersist to such an extent that the periphery of the hole continues toheat up due to the presence of the beam. But being in direct line ofimpingement, the bottom of the hole continues-to vaporize so long as thebeam is applied or until a hole is drilled through the workpiece.

The size, shape, as well as the depth of the hole, which are veryimportant factors for printing, created in this manner are dependentupon a number of interrelated factors. The amount of energy required tovaporize the volume of material to be removed consists not only of theamount of heat needed to take care of the heat of vaporization of thematerial, but also the amount required to raise that volume of materialto its boiling point and to replenish any heat which is lost to thesurrounding material during the time it takes to vaporize the givenvolume. In general, when using the extreme power densities andmicroscopic beam spot diameters which can be achieved with modernenergized beam equipment, the drilling of various materials can beaccomplished in a short enough time period to minimize the heat loss tothe surrounding material. Similarly, if only microscopic volumes ofmaterials have to be removed from the workpiece, the dwell time of thebeam over a given portion of the workpiece can be sufliciently short tominimize such side losses. The cutting or engraving of thin-sheetmaterials thus can be done fairly rapidly. On the other hand, if deepcuts are to be made, of for example .030, and the volume of the materialto be removed is substantial, then the cumulative dwell time of the beamover any particular spot of the workpiece becomes appreciable. For agiven power level and beam density the beam ON time must be appreciablylonger in order to supply the higher total heat required forvaporization of the larger volume of material which is to be vaporized.In such instances, thermal conductive influences can cause appreciableheat losses to the surrounding areas. One can, of course, go to higherbeam powers to compensate for these losses and/ or increase the beampower density by decreasing the beam spot diameter with a constant beampower or increase the beam power with the spot diameter kept constant.To do so, however, generally leads to more expensive equipment althoughit may tend to improve the cutting speed. Furthermore, there aredefinite practical considerations which limit the extent to which thisavenue for employing energized beams for the cutting of printing platescan be followed.

One of those practical problems, as illustrated in FIG- URE 14, residesin the actual thermal distribution within the vicinity of the beamimpingement area. Generally, the symmetrical distribution of the heatfrom the point of impingement depends to a large extent upon theprevious thermal history of the area, the uniformity of the thermalproperties of the material, the geometry of the workpiece as well as itsthickness and, of course, the uniformity of the energized beam itself.Under such circumstances there can be sufficient differences in theboiling rate, that is the vaporization about the periphery of the holebeing drilled, to cause a certain amount of raggedness in the shape ofthe hole itself. Recondensations around the edges can occur whichfurther accentuate the raggedness. What usually results in mostmaterials and is specifically more pronounced in some others, is a holethe edges of which are irregular and the shape of which is difficult tocontrol as is illustrated in FIGURE 15. There are several ways in whichthe raggedness can be smoothed, for example, where one goes to a smallerspot diameter and sweeps the hole circumference with the beam and thusaverages the irregularities. Another possibility is to repeatedly pulsethe beam over the same spot using short enough beam ON times and longenough OFF times to minimize thermal conductivity influences. A thirdpossibility would be to increase the beam power density to asufficiently high level that one very short burst of power is all thatis needed to drill the hole. But as previously mentioned, the latterwould be an expensive approach and the former increases the timerequired to make a printing plate with an energized beam.

Unsymmetrical thermal distributions have `a great imn pact on theenergized beam engraving process. If, for exn ample, the engraving is toconsist of a series of closely spaced holes, the degree of closeness oftwo adjacent holes is largely dependent upon the edge definition of theholes themselves. As illustrated in FIGURE 16, lack of thermal symmetrycan lead to breakovers between two adjacent holes. The combined effectsof hole edge raggedness and breakover forces one to keep the holes wellseparated, thereby reducing the lidelity and .resolution of the holepattern. The most obvious approach (aside from the techniques referredto earlier for controlling edge raggedness) that would overcome thisdifficulty would be to go to a smaller spot diameter and space the holescloser together but still sutiiciently far enough apart to precludebreakover. However, decrease in spot size is consistent with decreasingbeam power for any particular power density. Hence, unless power densityis increased as Well, one is faced with longer beam dwell times in orderto penetrate to a given depth in the material being engraved. This againis contrary to the goal of achieving high engraving speeds.

One solution proposed to solve this dilemma is to revert to a blankplate workpiece which has a low melting point. Materials frequentlymentioned are plastics and low melting point primary metals or eutecticsthereof. At first glance one would think that this would be a plausiblesolution since little power is needed to evaporate such materials.Hence, the cutting speeds could be increased to a high degree. Asidefrom the lack of durability in these materials which perhaps could beimproved somewhat by use of a higher strength backing material, there isan even more important reason why they do not fulll the bill as theworkpiece in a high speed engraving system. This has to do with thedegree of resolution which can be achieved on the resultant printingplate. The problem is again one of edge definition wherein the holeformed in the plastic material cannot withstand a large thermal gradientbefore it tends to disintegrate. Hence, even though the temperature atthe point is low enough to preclude vaporization, it may be high enoughto melt the edges and destroying the edge definition of leach hole asillustrated in FIGURE 17. One therefore tends to prevent this Iproblemby reducing the temperature at the edges, and again, the dwell time forproducing the printing plate has to be increased rather than decreased.

Although it has been suggested that the use of a backing material wouldresolve some of these ditiiculties because the backup plate wouldrapidly conduct the heat away from the hole edges before the edges couldmelt, it should be clear that any heat passing from the vaporizationregion must pass through the low melting material to reach the backupplate and therefore, in the absence of an enormous thermal conductivityof the top layer material, the speed of thermal transfer to the backupplate will be insuicient to prevent the destruction of the edges of theholes.

In summary, if a high melting point material is used as the workpiece inorder to withstand the high thermal gradients, the dwell time requiredto remove any appreciable amount of material is suiicient ly high tocause an undesirable spread of energy from the beam into the surroundingmaterial. Since there are no barriers to quench this spread of thermalenergy deposited by the energized beam, increased beam power to reducedwell time of the energized beam is required to compensate for theselosses.

Also, in the event a low melting point material is used on the workpiecein order to decrease the beam power requirement and decrease dwell time,the material surrounding the vaporization region is incapable ofwithstanding the high thermal gradients. Consequently, edge definitionbecomes poor and the delity of the engraved pattern deteriorates.

Furthermore, local irregularities in the thermal distribution patternaround the beam impingement area. foster Unsymmetrical and nonuniformvaporization thereby preventing the formation of smooth hole edges andleading to problems such as breakover between adjacent holes. If thehole separation is increased to compensate for this phenomena, thedensity of the pattern is reduced to an extent where the resolution ofthe pattern again has deteriorated.

Energized beams such as electron or ion beam devices and lasers areinherently high resolution tools. Resolutions on the order of one micronhave been achieved to date with such beams and better resolutions aretheoretically possible. If it is possible to utilize such highresolution tools and at the same time avoid the practical diiculties asdescribed heretofore, a substantial contribution to the printing art canbe made.

With these observations in mind, it appears that the energized -beamalone cannot eliminate these problems; hence, one must look to theworkpiece also.

It is an object of this invention to provide a hal'ftone printing plate.

It is another object of this invention to provide a printing plate onwhich high quality text material is inscribed in halftone.

It is still another object of this invention to provide a halftoneprinting plate through the use of an energized beam.

It is still another object of this invention to provide a method forestablishing intelligence with an energized beam on a blank plate havinga high density of dots uniformly distributed thereon.

It is still further an object of this invention to provide a method forestablishing intelligence on a blank plate having a plurality of minuteisolated projections.

It is a further object of this invention to provide a method forestablishing intelligence on a blank Iplate by removing portions of theworkpiece material which are isolated from one another.

It is a lfurther object of this invention to produce a blank plate forestablishment thereon of intelligence andy having a dense array ofprojections.

These and other objects of this invention will become more readilyapparent upon a review of the drawings and the description thereof asfollows. In the drawings:

FIGURE 1 shows a blank plate for engraving and with a plurality ofisolated projections.

FIGURES 2 and 3 show a method of making a printing plate from a blankplate as shown in FIGURE 1.

FIGURES 4, 5, 6, 7 and 8 show an alternate method for producing aprinting plate from a blank plate of the type shown in FIGURE l. n

FIGURES 9 and 10 show the preparations involved 1n producing a blankplate having a plurality of cavities lled with a second material.

FIGURES 11 and 12 show the method of producing intelligence on a blankplate of FIGURE by means of an energized beam.

FIGURE 13 shows the thermal energy spread from an energized beam duringan engraving operation.

FIGURE 14 shows the typical thermal gradients encountered in theworkpiece at the start of the engraving c cle.

yFIGURE l5 shows the ragged appearance of a cavity cut with an energizedbeam.

FIGURE 16 shows the breakover between adjacent cavities cut with anenergized beam.

FIGURE 17 shows the poor edge definition of a cavity cut with anenergized beam.

FIGURE 18 shows an enlarged perspective view of a relief letter engravedon a blank plate.

As will be obvious from the figures and the descriptions which follow,the use of the word blank in the terminology blank plate, as usedherein, refers to the fact that there is an absence of intelligence onthe plate initially and that said intelligence must then be added to theplate for it to become an actual printing plate.

Two types of blank plates for engraving thereon are described herein.Each is provided with a plurality of tiny dots (projections or cavities)which are isolated from one another. FIGURE l shows a blank plate havinga plurality of projections 10 each of which is isolated from itsadjacent projections by a groove typically presented at 12. Such a blankplate 14 may be manufactured from a smooth metallic plate made ofcopper, zinc, aluminum, magnesium or nickel and may be of any desirablethickness, but preferably with sucient bulk to be capable of absorbingand conducting away the thermal loads occurring during the evaporationof the projections with an energized beam. The top surface of the smoothmetallic plate must be fairly flat so that the projections 10 will havetheir top surfaces lying in a common plane. However, where variations inthe surface of the plate exist after the formation of the projections10, a further process for smoothing and flattening the projections intoa common plane could easily be carried out by conventional machining orstanding processes.

In the event that the blank plate 14 is curved for placement on aroller, then the top surfaces of the projections 10 must be equidistantfrom the base material from which they arise. In the case where theblank plate is part of a cylindrical section, then the tops of theprojections must lie on a surface substantially concentric with thecylinder. These latter conditions are necessary for eventual use of theplate with rotary presses.

The blank plate of FIGURE 1 may be made by an energized beam which hassufcient power and the diameter of which is sufficiently small so thatthe grooves 12 may be cut into the base material 16. By carefullycontrolling the relative movement of the plate 14 with respect to thebeam and with transverse cuts, isolated projections 10 are produced onthe plate 14. Common chemical removal processes may, of course, also beemployed to produce the blank plate 14.

An energized beam capable of cutting plate 14 could, for example, be abeam of charged particles as described in the patent to Steigerwald, No.2,793,281. The power density of the electron beam is adjusted so highthat it evaporates a small layer of the material on which it impinges.By repeatedly pulsing the beam in accordance with the teachings of thepatent to Steigerwald, No. 2,902,583, a well-defined hole may be made inthe workpiece material. Displacing the workpiece relative to the beamthen produces the grooves in the blank plate of FIGURE 1. It is, ofcourse, possible to make projections 10 in the blank plate' v14 havingdifferent shapes such as circular or oval or other shapes by the propercontrol of the plate relative to the beam. The grooves 12 can bearranged in different ways so that a triangular pattern of projections10 are formed. It should be realized, of course, that the time involvedin producing the blank plate 14 with an energized beam will besubstantial, depending primarily upon the type of material and volume tobe cut. However, the process for making the blank plates takes place offline so that the on line time of establishing intelligence on the blankplate is not affected. A multitude of these plates can be preparedbeforehand and stocked until needed.

The density of the projections in FIGURE 1 is so high that a sufficientnumber of individual imprints of dots can be made across the width of atypical character in a common text to permit the halftone printingthereof with high resolution.

Thus, one of the advantages of such a printing plate is that very tinetext material as well as pictorial material can be represented by a dotpattern. The use of dot halftones to represent pictorial material is acommon practice within the printing industry today. However, one has notbeen able to devise a practical system for representing very iine textmaterial in this manner. The problem becomes clear upon examining atypical line screen wherein dots are produced for the pictorialrepresentation in newspapers and where the dot diameters of the order ofve to ten thousandths of an inch. Typically, the widths of text lettersin todays newspapers are of the order of twelve thousandths of an inch.To represent a text letter by a pattern of these standard dots, it isnot possible to use more than one or two dots to cover this width. Theresultant effect isthat the text characters appear ragged and poorlydefined and unpleasing to the human eye.

The projections on the blank plate of FIGURE 1 have a much linerresolution so that even small text characters such as 12 points or lessmay be printed in halftone. The top surface areas of the projectionsthat will be used to carry ink should -be no less than 16x106 squareinches and normally are 1 to 9 l06 square inches with groove widthsapproximately from to 10X10"4 inches. Exact sizes and spacings dependupon the type of paper and ink used during printing, and consequently,all text material may be produced in halftone on the plate withsignificant resolutions.

Furthermore, there is a distinct advantage in having the entire printingsurface initially covered with these projections. For instance, severalareas on the printing surface may be designated for bright tones such aswhite and the ink carrying projections must be removed from these areas.If these white areas are large, the paper on which the print is to bemade may dip into these areas and contact the base material and pick upany stray ink present thereon.

Prior art techniques avoided this problem by depressing or etching theseareas down at. least .030 inch below bordering raised printing surfaces.These deep cuts are not needed any longer with the printing plate ofFIGURE l. By providing these large white areas with widely spaced,discrete, microscopic projections, the paper bridges these large areaswithout the usual sagging and resultant ink pickup from the depressedsurfaces. Since the projections are so minute their imprints will affectthe coloring of the white areas very little and at most provide thepaper with a very light gray background. As a result, one may make aprinting plate from the blank plate of FIGURE 1 with projections asshort as .002 to .003 inch and generally less than .005 inch.

The beam 20 is generated with a device as shown in Patent No. 2,793,281and directed at the blank plate 22. The power and the power density ofthe beam 20 are arn justed together with the focus of the beam at theplate so that individual projections may be removed by the beam. FIGURE2 shows the beam 20 evaporating the projection 24, and projections suchas 23 have already been evap orated. The control of the movement of thebeam 20 relative to the blank plate 22 and its intensity will causepreselected projections to be evaporated. A final configuration such asthe letter T in FIGURE 3 is made wherein the T is produced in relief andconsists of minute dis-1 crete projections.

The beam spot size may be as small :as one micron in diameter, butgenerally will be adjusted to a size corn-s mensurate with the size of aprojection. With such a beam size, one projection may be evaporatedwithout affecting adjacent ones. Generally the dots of the blank arealso chosen to have surface areas commensurate with normal beam spotsize and acceptable printing speeds.

Generally the plate 22 is made of sufficient bulk and of a good thermalconducting material so that the heat lost to the lplate during theremoval of any one projection will not affect adjacent projections. Theprojections are effectively thermally isolated from one another.

Herein resides one of the unique advantages of this invention. Theapplication of inherent high resolution halftone characteristics to ablank plate beforehand makes possible the subsequent engraving thereonwith an ener-= gized beam such as an electron beam, ion beam, or laserwithout the previously mentioned disadvantages.

The height of the projections and their cross-sectional areas areoptimized keeping in mind the type of material, the desired printingspeed and the method of printing. Where an energized beam such an anelectron beam is used, its power, power density, spot size and intensityare preferably controlled to allow removal of a projection 'with asingle pass. The shape of a projection bears a strong factor on this andits height-to-average-width ratio is general-= ly held to less thanthree. For practical height .003 inch apn pears acceptable. The ratio,however, should not then become too large lest the projections becometoo slender and incapable of standing up under a printing pressoperation.

FIGURES 4 through 8 show an alternate method inn volving a chemicalremoval process for using a blank plate of FIGURE l. The optimum heightand cross-sectional dimensions of the projections now are determined byother considerations than when an energized beam issued. There areunique advantages also in the chemical removal of the projections.

The blank plate 14 in FIGURE 4 is rst covered with a chemical resistmaterial 30. Material 30 may be, for instance, a lacquer, acid-resist ora standard photoresist material such as KPR which becomes insoluble to arinse after exposure to either light passing through a photographic 32or exposure by an energized beam which is modulated as it passes overthe material. The material 30 will cover all of the projections as wellas the grooves and form a smooth layer across the whole of the plate 14.

After exposure in FIGURE 4, the material 30 will have an exposed T, 34and an unexposed section 36. FIGURE 6 shows the cross-sectional View.

Thereupon the unexposed section 36 is rinsed away in a bath to which theexposed T is not affected. The underlying projections of section 36,being stripped of their protec tive coating, may then be chemicallyremoved by insertion in a strong etching bath. The final cross-sectionalview after etching is shown in FIGURE 7. Note that the material 38protected the projections completely with but minor inconsequentialundercutting occurring adjacent to the foot of projections 40 and 42.

Subsequently, the protective material is removed and the exposedprojections show the letter T in FIGURE 8. It should be clear that thecoating material 30 need not be a photosensitive one when a high powerdensity beam such as an ion, electron, or laser beam is used to exposethe plate. The material 30 need only be resistive to the etchant to beused in subsequent chemical removal process, with the high power densitybeam being used to selectively remove the coating over those projectionswhich are to be chemically eliminated from the matrix plate. Note thatthe particular advantage of using a blank plate as in FIG- URE l in thechemical removal. process of FIGURES 4 through 8 is the substantialavoidance of undercutting problems. The tops of the projections 40 and42 are protected since the protective coating 38 extends down to thebase material. In the event the protective material covers a portion ofthe top of a projection, undercutting thereof will, of course, occur.But the adjacent projection will fully be protected and thedeterioration of one projection will not materially and visibly affectthe delity of the text material. This advantage will-become clearly ap`1parent where the area density of the projections are so high (forexample. projections of 4 106 square inches in area and separated by.0005 inch), that the loss of a row of projections on each side of atext character will not affect its fidelity. Very fast etching baths maybe employed with`= out concern with undercutting.

The need for paper supports on large etched areas may be served byleaving every seventh or eighth projection intact in these wide areashaving less than 5 percent grey tone. When using a photographic negative32 to expose the plate, this may be accomplished by incorporating abackground of dots of appropriate size and spacing in the negative.Where an energized beam is used to expose the material 30, the Ibeam maybe so controlled as to be modulated periodically to an OFF state,thereby leaving a pattern of widely spaced unexposed projections in thebackground areas of the plate. Said modulations would be superimposed onthe variable modulations carrying the intelligence to be imparted to theplate.

Another method for providing a printing plate contain-1 ing isolatedareas is illustrated in FIGURES 9', l0, ll and l2. A blank plate isprovided with a multitude of isolated cavities 62 which are separatedfrom one anu other by land areas 64. These land areas are made up of thebasic material from which the printing plate is made and provide a fenceor barrier between the various cavities. These cavities, as shown inFIGURE 10, are iilled with a second material 66 that is different fromthe material from which the blank plate 60 is made up and has a lowermelting point or a lower evaporating point. A typical material thatcould be used for lilling the cavities 62 is a low melting plastic.After the cavities have been filled with the lovver melting material 66,an energized beam 70 is applieduto the plate with such power and powerdensities that if can readilyl evaporate the material 66 within thecavities without melting or affecting the base material of the blankplate. Since the energized beam 70 has a small cross section, it iscapable of evaporating the lower melting material in one cavity withoutaffecting the material in adjacent cavities. Any heat imparted by thebeam onto the blank plate 60 is readily carried away from the cavity tothe base metal without upsetting the temperature in the adjacentcavities which are therefore eifec tively thermally isolated. A blankplate provided with the low melting material contains a high density ofcavities for the same purpose as the blank plate 14 in FIGURE 1. Uponthe removal by the energized beam of the low melting material and theformation of characters such as the letter T in FIGURE 12, an intaglioprinting process can be applied whereby the ink is carried in thecavities and imparted to the printing paper according to standardprinting processes. The cavity depth, size, and other characteristicscan be determined beforehand based upon the type of ink and paper to beprinted with. The plate can be made up from a very ne screen mesh havinga smooth top surface so that all of the cavities have their entranceslocated in substantially the same plane.

The material 66 is applied to the printing surface of the blank plateand is substantially ush therewith.

A sandwich-type construction could also be used in this instance toprovide a base plate for good heat sink qualities. The lower layer ofthe sandwich could be removed after the cutting operation so as to leavea pattern of very small through-holes, in other words, a screen pat-Itern for screen-type printing. Again it should be realized that theshape of the cavities need not be rectangular or that the cavitiesshould be arranged in any particular recm tangular pattern. In fact, toobtain optimum thermal isolation and the highest packing density of thecavities, a triangular array is the preferred geometry. In such an arrayany three adjacent projections would be equidistant from one another.The triangular array is a welll-known geometry for high density packingand is described in moreJ detail in Slater, Introduction to ChemicalPhysics 415 (1st ed. 1939).

In FIGURE 18 a letter t is shown made up from a plurality of projectionsarranged in a square array. The letter t is greatly exaggerated toprovide an indication of the perspective of a relief text character madeaccording to this invention.

The methods described in relation to FIGURES 9 through 12 whereindissimilar materials are used to pro-1 vide isolation between theindividual printing dots require a very small amount of power where anelectron beam is used to evaporate the material with the lower meltingpoint. Hence, the dwell time of the beam can be exceedingly low, leadingto very high engraving speeds. The total beam power requirement may bequite modest, such as 100 watts for materials 66 like parafiin, etc.,and with dwell times of the order of 100 microseconds or less. Theseparameters are well within the capabilities of presu ent electron beamequipment and may very soon be available in other precision, energizedbeam devices, such as laser and ion beams. The printing plate has thefur ther advantage in that it is reusable so that it may again be filledwith the secondary material to make up a new blank plate.

It is to be understood that the invention is not limited l0 to thespecific embodiments herein illustrated and described but may be used inother ways without departure from its spirit as defined by the followingclaims.

I claim:

1. A printing plate blank comprising:

a blank plate provided with at least one surface working area for theplacement thereon of intelligence,

said surface working area covered with a plurality of minute separateprojections each having a minute surface area less than 16 10r6 squareinches,

said projections being substantially alike in shape and height and beingsubstantially uniformly distributed over said surface working area, theseparation of the surface areas being no greater than 10 104 inches toimpart high resolution halftone character istics to the blank plate.

2. A device as recited in claim 1 wherein each proiection surface areais substantially at to accept ink thereon.

3. A device as recited in claim 1 wherein the blank plate is curved andthe projection surface areas lie on a surface substantially parallel tothe curve of the blank plate.

4. A device as recited in cla-im 3 wherein the blank plate is shape-dand curved as a section of the curved surface of a cylinder and thesurface areas of the projections lie substantially in a cylindricalsurface concentric with the cylinder.

5. A device as recited in claim 1 wherein the projections are uniformlydistributed over the entire surface working area according to apredetermined pattern.

6. A device as recited in claim 5 wherein the projections aredistributed in a triangular pattern.

7. A device as recited in claim 1 wherein the height of 'the projectionsis approximately or less than .O05 in.

8. A printing plate blank comprising:

a blank plate made of a base material having good thermal conductivityand provided with at least one surface working area for the placementthereon of intelligence,

said surface working area being covered with a plurality of separateprojections each having a, minute surface area at the top of theprojections,

the base material of said blank plate having suilicient bulk toeffectively thermally isolate adjacent projections, p

the minute surface area of the projections being substantially at,substantially equidistant from said base material, and beingv less than16x10-6 square inches, and

the spacing between the surface areas being no greater than 10X 104inches to impart high resolution halftone characteristics to the blankplate.

9. A device as recited in claim 8 wherein the height of the projectionsis approximately or less than .005 inch.

10. A device as recited in claim 9 wherein the ratio of the height ofeach projection to the average-width of each projection is less thanthree.

11. A master halftone printing plate with supports for the material tobe printed on comprising:

a single printing plate having its entire printing surface covered withhalftone intelligence thereon,

said printing. surface being provided with relief text material andblank spaces,

said text material including a plurality of minute, separateprojections, having a top surface area less than 16 l06 square inchesseparated by no ,more than 10X 10-4 inches, and

said blank spaces including minute separate widely spaced projections tosupport the material.

12. A device as recited in claim 11 wherein the blank spaces include aplurality of widely spaced uniformly distributed projections.

13. A device as recited in claim 11 wherein the area l l density of theprojections in the blank spaces is less than percent greytone.

14. A device as recited in claim 13 wherein the height of theprojections is approximately or less than .005 inch.

15. A master printing plate for printing on paper or other thinmaterials comprising:

a single printing plate having a printing surface entirely covered witha plurality of minute projections each having a height no greater than.005 inch a-nd a surface area on top less than 16x10-6 square inches,

the area density of the projections varied to form rem lief printings,the separation between projections being no greater than X104 inches in100% greyn tone regions of the printings, and

where the density of the projections between the printings is decreasedto a level no greater than 5% greytone for sharp contrast and forsupport of the material being printed upon,I

16. A method for making a printing plate comprising generating anenergized beam,

directing the energized bea-m at a blank plate having a printing surfaceentirely covered with a plurality of minute, thermally isolatedprojections,

moving the blank plate relative to the energized beam,

adjusting the power and the power density of the ener" gized `beamwithin a range suicient to remove a projection, and

selectively deenergizing the beam as the blank plate moves relative tothe beam to preserve preselected projections.

17. A method as recited in claim 16 and further inm cluding:

adjusting the cross-sectional area of the energized bea-m at theprinting surface to be commensurate with the cross-sectional area ofaprojection..

18 A method for making a printing plate comprising:

generating a beam of charged particles,

focussing the beam on a blank plate having a printing Surface entirelycovered with a plurality of minute, thermally isolated projectionshaving crossesectional areas no greater than 16x106 square inches,moving the blank plate relative to the beam of charged 5 particles,

adjusting the power and the power density of the beam `within a rangesufficient to remove a projection with out affecting adjacentprojections, and selectively deenergizing the beam as the blank platemoves relative to the beam to preserve preselected projections, 19., Amethod as recited in claim 18 wherein the focussing step furthercomprises:

adjusting the focus of the beam of charged particles to produce a spotsize of the beam at the printing surface that is commensurate with thecross-sectional area of a projection.I 20. A method as recited in claim16 wherein the projectons are separated by a `distance no greater than10X10-4 inches Iand have cross-sectional areas less than 16x10* squareinches and the beam cross-sectional area is adjusted to be commensuratewith the cross-sectional area of the projection,

References Cited UNITED STATES PATENTS 384,586 6/1888 Norman. 1,459,6696/1923 Berold lOl-395 2,234,997 3/1941 Yanes lOl-401.1 XR

FOREIGN PATENTS 866,070 4/1961 Great Britain.

t: DAVID KLEIN, Primary Examiner U.Sc Cl. X.R.

96-36.3, 86; lOl-401, 401.1; l78-6.6; 219-69, 121; 346-76

